In a common mobile communication device, matching impedance networks of a power amplifier, such as a broadband pulse amplitude modulation power amplifier, in a radio frequency circuit are all paired in a customized manner. Once there is a need for a replacement with a different power amplifier, the customized matching impedance network also needs to be replaced accordingly, which increases the production cost. In view of this, the present invention proposes an impedance adjusting device and a mobile phone device applying the impedance adjusting device.